Vector $\overline{M}$ lies in the xy plane making an angle of θ above the positive x-axis. Vector $\overline{N}$ is lying in the same plane making an angle Φ below the positive x-axis. Determine their dot product.

Hint: Use one of the following identities-

cos(A + B) = cosAcosB - sinAsinB

cos(A - B) = cosAcosB + sinAsinB